Geologic time frame is a term used to describe the vast span of Earth's history, which is divided into four major eras: the Precambrian, Paleozoic, Mesozoic, and Cenozoic. The Precambrian ERA is the longest, spanning from 4.6 billion years ago to 541 million years ago. The Paleozoic ERA followed, lasting from 541 million years ago to 252 million years ago. The Mesozoic ERA was next, lasting from 252 million years ago to 66 million years ago. Finally, the Cenozoic ERA began 66 million years ago and continues to the present day.